Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$91.46	13.236%	$103.5656	$103.57	$103.55	$103.60
Purchase #2	$117.81	7.344%	$126.462	$126.46	$126.45	$126.50
Purchase #3	$62.32	5.770%	$65.9159	$65.92	$65.90	$65.90
Purchase #4	$227.28	6.789%	$242.71	$242.71	$242.70	$242.70
Purchase #5	$144.94	13.486%	$164.4866	$164.49	$164.50	$164.50
Purchase #6	$76.58	12.571%	$86.2069	$86.21	$86.20	$86.20
Purchase #7	$36.89	6.143%	$39.1562	$39.16	$39.15	$39.20
7 purchase totals =	$757.28		$828.5032	$828.52	$828.45	$828.60